Undercooling Behavior and Solidification Microstructure Evolution of Sn-Cu-Ni Solders Modified by Minute Amount of Mixed Rare Earth La-Ce
Sn-Cu-Ni alloy solders have attracted considerable attention from electronic packaging manufacturers and suppliers owing to silver- and lead-free feature and low-cost advantage of the solders. However, there is still a lack of in-depth understanding on composition optimization and microstructure control of the solders. In the present study, the influences of the addition of a minute amount of mixed rare earth La-Ce, in the range of 0.05-0.50wt%, on melting characteristics, undercooling behavior and solidification microstructure evolution of Sn-0.7Cu-0.05Ni-xMRE (x=0.05, 0.10, 0.25, 0.50wt%) alloy solders were investigated. The results show that the addition of rare-earth La-Ce has brought about an obvious decrease of the undercooling for Sn-Cu-Ni series of solders, consequently the growth of primary solidification phase of Cu(Ni)-Sn type intermetallic compound has been suppressed and the β-Sn phase has exhibited a microstructural transition from dendritic grain to equiaxed grain with increasing the amount of La-Ce added to the solder.
Jian-Feng Nie and Allan Morton
M. B. Zhou et al., "Undercooling Behavior and Solidification Microstructure Evolution of Sn-Cu-Ni Solders Modified by Minute Amount of Mixed Rare Earth La-Ce", Materials Science Forum, Vols. 654-656, pp. 1373-1376, 2010